Explicity import <memory> in PackSample.cpp (#564)

It looks like earlier, this was depending on one of the headers it
imports to import <memory> to provide unique_ptr; however, this is not
necessarily the case, so it needs to be explicitly imported.

sample/PackSample/PackSample.cpp

@@ -6,6 +6,7 @@
 #include <iostream>
 #include <vector>
 #include <map>
+#include <memory>
 #include <queue>
 
 #ifndef WIN32